For example, as a scheme for realizing high speed signal transmission within one electronic device or between electronic devices arranged at a relatively short distance (e.g., within a few cm to 10 or more cm), for example, LVDS (Low Voltage Differential Signaling) is known. However, with the large capacity and high speed of recent new transmission data, problems such as increase in power consumption, increase in influence of signal distortion due to, for example, reflection, increase in unnecessary radiation, and the like have arisen. For example, when a signal such as an image signal (including a capture signal) or a computer image is transmitted at a high speed (in real time) within a device, the LVDS reaches its limit.
There is a scheme of reducing a transmission speed of each signal line through signal parallelization due to an increased number of lines in order to cope with the problem of the high speed of transmission data. However, in this scheme, the number of I/O terminals increases. As a result, a printed board or cable lines become complex or a large size of a semiconductor chip is necessary. In addition, high speed and large capacity data is along a line, which causes a problem known as electromagnetic interference.
Problems associated with the LVDS or the scheme of increasing the number of lines are caused by signal transmission using electrical lines. As a scheme for resolving the problems caused by the signal transmission using the electrical lines, a transmission scheme without electrical lines has been proposed.
For example, a technique for wirelessly performing in-housing signal transmission and applying a UWB (Ultra Wide Band) communication scheme has been proposed in Japanese Patent Laid-open Publication No. 2005-204221 or 2005-223411. In the UWB communication scheme disclosed in the two Patent Literatures, there are problems in that a carrier frequency is low, the UWB communication scheme is not suitable for high-speed communication such as image signal transmission, and an antenna is large. Further, since a frequency used for transmission is close to another frequency of baseband signal processing, there is a problem in that it is easy for interference to occur between a radio signal and a baseband signal. In addition, when the carrier frequency is low, it is easy to receive influence of a driving system noise in a device, and a solution becomes necessary.
On the other hand, use of a carrier frequency in a millimeter wave band is disclosed in Japanese Patent Laid-open Publication No. Hei10-256478 or U.S. Pat. No. 5,754,948. When the carrier frequency in a millimeter wave band with a shorter wavelength is used as in the two Patent Literatures, problems of an antenna size, interference, or influence of a driving system noise can be resolved.